606 
ME. W. K. PAEKEE ON THE STEUCTUEE AND 
called turbinals ; and yet, simple as these structures are, they are not easy to under- 
stand or to describe. In front of the girdle-shaped ethmoid three large cartilaginous 
growths project. The median growth is a vertical plate, the unossified continuation of 
the perpendicular bone ; this is the septum nasi ( s.n .). On each side of this middle 
wall the sinuous enfoldings of the olfactory or Schneiderian membrane lie. The open- 
ings into this labyrinth, or outer nostrils (fig. 3, e.n.), lie at a good distance from the 
septum, at its fore end. The openings by which this labyrinth communicates with the 
cavity of the mouth, the inner nostrils (fig. 4, i.n.), are also a good distance apart, oppo- 
site the hinder part of the septum, at least behind its middle. Now, unlike the eye- 
balls, which are permanently separate, and the ear-balls, which were so at first, but lose 
their independence, the nasal sense organ has no independent growth of cartilage; 
the main part is borrowed from the trabeculee cranii, and the rest from the upper 
labials. 
For in the ethmoidal region the coalesced trabeculse (see the early stages in Plate 55, 
soon to be described) not only grow together to form an 4 internasal plate,’ but behind 
this part, from their edges, a cartilaginous growth proceeds, which fills in all the inter- 
space up to the hinder or parachordal region of the skull floor. Then, besides this, 
they grow up into a wall on this side and on that ; and not only grow into side walls, but 
also develop cartilage, which divides the cranial from the nasal chambers, building in the 
foregrowing olfactory nerves [crura). Below, the nasal labyrinth is well floored; above, 
very imperfectly (figs. 3 & 4). 
In the larvge, as we shall see (Plate 55, tr.), the trabeculse flatten out, and straighten 
out, instead of keeping the down-bent form acquired during the existence of the ££ meso-. 
cephalic flexure.” The flattening out of these bands is similar to what we see in the 
Shark. The internal nostrils (fig. 4, i.n.) set bounds to these right-and-left laminae 
towards the hinder third ; they then become very large and leafy, each leafy plate send- 
ing out two lateral claws, one pointed and looking backwards, and the other obtuse and 
stretching forwards and outwards. Then, all of a sudden, the trabeculae cease to grow, 
and their terminal part, or ££ cornua,” project forwards and look inwards from the middle 
of the rounded fore edge of the nasal floor. These ££ cornua trabeculae ” are Professor 
Huxley’s prorliinal cartilages. These distal ends of this basal part are much smaller 
in the Toad than in the Bull-frog and our native kind (figs. 1 & 2, c.tr.). 
From the broad, double, concave floor arises the partition wall, or septum nasi [s.n.), 
and from this wall a roofing-plate, right and left (fig. 3, al.s.). This roofing-cartilage 
is scarcely a third as broad as the floor, whereas in the Frog (figs. 1 & 2) it is the larger 
of the two. It is wider behind where it runs into the aliethmoid ; and also in front 
it spreads, thickens, and shelves over into an oblique front wall, which has two round 
windows close to the front of the floor for the exit of the nasal nerves (fig. 5, al.n., n.n., 
c.tr.). On each side of these openings the outer nostril [e.n) is guarded by a thick, oval 
leaf of cartilage, the “1st labial” (figs. 3, 5, 6, u.l.'), a segment from the large single 
piece seen on each side in the Tadpole (see “ Frog’s Skull,” plate v. u.l.). This cartilage 
